1. Field of the Invention
The invention relates to a plant for the use of exhaust gases of an electric melting furnace for steel.
2. Brief Description of the Background of the Invention Including Prior Art
Plants for the use of the heat content or, respectively, for cleaning of exhaust gases of electric melting furnaces are known, for example, from the German Patent DE-PS 3,214,300, the German Patent Application Laid Open DE-OS 1,804,098, as well as the German Patent Application Laid Open DE-OS 3,121,860. In these references, the hot furnace gases are fed to a station for preheating of the charging scrap. It is further known to operate such plants in connection with a plant for the separation and collection of dust from the exhaust gas.
It is further known to dedust by secondary cleaning the air of a shop which contains such a melting furnace. It is also known from the state of the art to provide a casing around electric melting furnaces for steel production from scrap. Both a substantial decrease of the noise molestation at the working place and in the environment and surrounding of the plant as well as a more effective capturing of the dust and gas emission from the furnace is thereby achieved. In order to capture the dust emission, an amount of gas is sucked over a so-called fourth roof hole from the oven via a water-cooled pipe band with adjustable coupling box for adjustment of the combustion air volume required for post-burning of the carbon monoxide-containing oven exhaust gases for capturing of dust emission. In general, the post-burnt exhaust gas volume from the fourth roof hole amounts to about 1000 m.sup.3 n/h and ton of oven capacity. In order to control the exhaust gas cleaning to a value prescribed by environmental regulations, for example by TA-Luft 86 in the Federal Republic of Germany, of 20 mg/m.sup.3 n in a filtering collector, this exhaust gas is cooled to 140.degree. C. The tubular coolers corrode very quickly due to the aggressiveness of the exhaust gases. Acrid smelling and harmful smokes are generated in the context of the usual scrap preheating by carbonizing at low temperature of organic components in the scrap, such as oil, lacquer, and plastics, which smokes cannot be collected in the filter. For this reason, a cooling of the exhaust gas by a cooler or a scrap preheating is frequently dispensed with and the required low exhaust gas temperature is achieved by an increase in the cold air admixture, i.e. substantially more air is sucked off from the casing than would be required for capturing the secondary dust emission. This method of operation, however, is unsatisfactory, because the filter is continuously subjected to an unnecessarily high exhaust gas volume, because the waste heat is not used for preheating the scrap and thus for energy saving of the current required for melting, and because, in addition, the transport of additional cold air requires a higher energy use of the exhaust blowers.
The disposal of oil or, respectively, water-containing roll sinter mud is a problem which was conventionally solved by adding such roll scale to agglomeration plants for the generation of a blast furnace sinter. The electric filter cleaning plants present in such agglomeration plants have however been frequently destroyed by filter fires based on the oil-containing vapors. This disposal method is therefore no longer available. A chemical preparation and treatment of these roll sinter muds cannot be justified on economic grounds.
However, the cleaned roll sinter muds form an excellent starting material for electric melting furnaces.